Year 2026 / Volume 118 / Number 2
Original
Relative fat mass and constipation in United States adults ‒ A cross-sectional study of 11,380 participants from NHANES 2005-2010

74-82

DOI: 10.17235/reed.2025.11391/2025

Min Lv, Xiaxi Wu, Wei Wang,

Abstract
Background: constipation is a common gastrointestinal disorder closely associated with obesity. Relative fat mass (RFM) is a newer anthropometric index that offers a more precise reflection of body fat distribution than traditional methods. Despite its advantages, the potential link between RFM and the likelihood of experiencing constipation has not been thoroughly examined. This study was therefore designed to explore the association between RFM and constipation Methods: data were obtained from the 2005-2010 cycles of the National Health and Nutrition Examination Survey (NHANES). Constipation was defined using the Bristol Stool Form Scale and questionnaire responses. Weighted multivariable logistic regression models were employed to evaluate the association between RFM and constipation. Propensity score matching (PSM) was used to balance baseline covariates between groups. Analyses were conducted both before and after PSM to test the robustness of the findings. Smooth curve fitting and threshold effect analyses were conducted to explore potential nonlinear relationships. Subgroup analyses and interaction tests were used to assess possible heterogeneity across different population strata. Results: a total of 11,380 participants were included in the final analysis, among whom 1,206 were classified as having constipation. Logistic regression revealed that in the fully adjusted model, each one-unit increase in RFM was associated with a 2.9 % reduction in the odds of constipation (OR = 0.971, 95 % CI: 0.956-0.986, p = 0.0011). Furthermore, PSM analyses confirmed the robustness of the results. The inverse association between RFM and constipation was more pronounced among individuals aged > 45 years, those with hypertension, and those who did not consume alcohol (all p for interaction < 0.05). Smooth curve fitting and threshold effect analysis indicated a nonlinear relationship, with an inflection point at an RFM of 36.06. Conclusion: our study suggests a significant inverse association between RFM and constipation. Further prospective studies are warranted to validate this relationship.
Lay Summary
Constipation is a common gastrointestinal problem that can seriously affect a person’s quality of life. While many studies have explored its potential causes, the relationship between body fat and constipation remains unclear. In this study, we used data from a large, nationally representative health survey in the United States to investigate whether relative fat mass — a body composition index that better reflects actual fat levels than body mass index — is associated with constipation in adults. We analyzed data from over 10,000 participants aged 20 years and older. Participants were divided into groups based on their reported bowel habits, and their body fat levels were calculated. We used advanced statistical techniques to examine the association between body fat and constipation, while accounting for other factors such as age, gender, diet, physical activity and health conditions. We found that people with higher body fat were less likely to experience constipation. This association remained significant even after adjusting for a wide range of influencing factors and using matched samples to ensure comparability between groups. Our findings suggest that body fat may play a role in bowel function, although the exact mechanisms are not yet clear. Understanding this relationship could help improve prevention and management strategies for constipation, especially in populations at risk.
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Lv M, Wu X, Wang W. Relative fat mass and constipation in United States adults ‒ A cross-sectional study of 11,380 participants from NHANES 2005-2010. 11391/2025


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Publication history

Received: 04/06/2025

Accepted: 22/07/2025

Online First: 29/09/2025

Published: 09/02/2026

Article Online First time: 117 days

Article editing time: 250 days


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